This invention relates generally to apparatus for launching spheres into liquid pipelines, and particularly to meter provers making use of such apparatus.
U.S. Pat. No. 3,911,724 issued Oct. 14, 1975, discloses apparatus which can be employed for introducing spheres into a line, and which when incorporated in a meter prover of the unidirectional type becomes an interchange which receives a sphere from the outlet end of the metering loop and causes it to be launched into the inlet end of the loop to commence a meter proving run. The apparatus makes use of a shuttle assembly which is reciprocated between sphere receiving and launching positions, and which operates within a body which forms a connection between the outlet and inlet ends of the metering loop. The shuttle assembly includes a plunger which establishes a seal for the interchange body when the shuttle means is in or near sphere launching position. It also includes a sphere carrier which receives the sphere when it is delivered from the outlet end of the metering loop. It serves to transport the sphere from sphere receiving to sphere launching position by reciprocation of the shuttle assembly. The sphere carrier also has means which prevents substantial backflow of liquid through the interchange when the shuttle assembly is in sphere receiving position. In the embodiment disclosed in said patent the means for controlling backflow through the interchange consists of a circular flow restricting baffle or barrier which is formed as a part of or is mounted on the sphere carrier, and which in the sphere receiving position of the shuttle means is positioned within a sleeve that is carried by the body and which cooperates with the plunger assembly.
One characteristic of the embodiments disclosed in said patent is that the backflow control means restricts badkflow but does not provide an interchange seal. Also parts of the shuttle assembly may be forced out of alignment with the axis of the body, particularly when the apparatus is made in the larger sizes (e.g., for handling spheres of from 20 to 40 inches or more in diameter).